There are many many reasons for insects. Some of them have functions that are less obvious, but many have very vital functions in nature, even if it is just that they serve as food for many other creatures. I can guarantee you, many bird species alone would go extinct without insects! Many insects pollinate various plants.. I know there are some exotic flowers and plants that have particular features to attract one type of insect in order to pollinate itself. Without flies, there would be carrion and rot all over the place . Many other insects help keep down populations of smaller insects. I'm sure I have only barely touched upon all the things they do.

But anyway, the bottom line is YES! Our world would be in chaos without them!